1. Field of the Invention
The present invention relates to a display control circuit for drivingly controlling a display device.
2. Description of Related Art
A conventional LCD (liquid crystal display) panel for a display device is disclosed, for example, in Japanese. Patent Laid-Open No. 9-138670. Referring to FIG. 14, the conventional LCD panel will be described below.
FIG. 14 illustrates a display panel 30 and a display control circuit 9 for displaying data on the display panel. The display control circuit 9 includes a gamma circuit 10 and gray scale selection drive circuits 29-1 to 29-N, where N is the number of pixels for one line of the display panel. The gray scale selection drive circuit 29-1 includes a decoder circuit 24-1, a gray scale selector circuit 22-1 and a drive circuit 49-1. Each of the gray scale selection drive circuits 29-2 to 29-N has the same configuration as the gray scale selection drive circuit 29-1, the description of which is omitted. A portion subsequent to a symbol “−” indicates its circuit number and is omitted for description if the circuits are not required to be distinguished from each other.
The display panel 30 can be modelized as a panel load for each drive line. The panel load 31 can be simulated by a resistor 34 and a capacitor 35.
The gamma circuit 10, as illustrated in FIG. 2, includes resistors R1 to R16 and switches S1 to S16. Resistors R1 to R16 are connected in series and reference voltages Vref1 to Vref2 are resistively divided to produce gray scale voltages V1 to V16. That is, gray scale voltages Vi and Vi+1 are produced across a resistor Ri. Gray scale voltages V2m and V2m−1 are outputted into one gray scale wiring VTm as a result of switches S(2m) and S(2m−1) being switched by a gray scale change-over timing signal. In other words, the gamma circuit 10 switches the gray scale voltages to even-numbered gray scale (2m gray scale) and odd-numbered gray scale (2m−1 gray scale) for output. The switching is performed with the gray scale change-over timing signal CK as a synchronous signal and the gray scale voltages V2m and V2m−1 undergo time division multiplexing to be transmitted through the gray scale wiring VTm.
A decoder 24 outputs a gray scale selection signal DT indicating a gray scale to be selected into a gray scale selector circuit 22 on the basis of a display data D and a gray scale change-over timing signal CK. The decoder 24 outputs a switch change-over signal φ for controlling switching of a switch 48 into a drive circuit 49.
The gray scale selector circuit 22 outputs a selected selection gray scale signal VTM into the drive circuit 49. The drive circuit 49 includes an amplifier 41 and the switch 48. The amplifier 41 power-amplifies the selected gray scale signal VTM. The switch 48 outputs a driving signal VO outputted from the amplifier 41 at a timing based on a switch change-over signal φ.
The driving signal VO is transmitted to the display panel 30 and charges and discharges a capacitor 35 through a resistor 34. The brightness of a pixel varies with a voltage of the capacitor 35, so that a display data is displayed.
This conventional display device displays a display data on the panel using a pre-charge period for pre-charging a pixel 31 and a data display period corresponding to a pixel data.
During the pre-charge period, the gray scale selector circuit selects and outputs a gray scale voltage corresponding to a predetermined even-numbered gray scale V2m of gray scales corresponding to data. Accordingly, a voltage of an even-numbered gray scale corresponding to a display data is transmitted to the display panel 30 as a driving signal VO. The voltage of the transmitted driving signal VO is held in a capacitor/wiring capacitance 35 of the display panel 30.
Subsequently, with a data to be displayed having an even-numbered gray scale V2m, the switch 48 is released during a data display period. Releasing the switch 48 shuts down driving of the drive circuit 49 for the display panel 30, thus holding a voltage held in the wiring capacitance 35 of the display panel 30. On the basis of the voltage, a display data is displayed.
With a data to be displayed having an odd-numbered gray scale voltage V2m−1, the switch 48 is kept closed during a data display period. The gray scale selector circuit 22 outputs the odd-numbered gray scale voltage V2m−1 in accordance with data and the outputted voltage is transmitted to the display panel 30 as a driving signal VO through the drive circuit 49. On the basis of the voltage of the driving signal VO, a display data is displayed.
A gray scale voltage Vi corresponding to the display data D is transmitted to the display panel 30 in this way. However, an even-numbered voltage V2m is displayed during a data display period, no electric current is transmitted from a driver 9 because the switch 48 is off. Accordingly, a voltage of a wiring capacitance 35 may be changed by a leak current generated on the display panel 30 side. This causes a problem of generation of a color error.